Adjusting Fuel Mixture
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Adjusting Fuel Mixture
I have a 1979 Ford F150 and I am trying to adjust the mixture of fuel into the carb, I failed My DEQ test and i have to lower the CO, How can I do this, were are the mixture screws? Motor is a 351 M
MSEE
Joined: Apr 2004
Posts: 10,386
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From: Austin, TX
The mixture screws are on the front of the carb, underneath the fuel bowl. Turn them out to go rich, and in to go lean. Be very careful with this setting. The proper way to make this adjustment is with a vacuum gauge. Be aware that this only adjusts the mixture at idle. It's not likely that this one adjustment will help you pass emissions. To pass emissions, you need to verify all emissions equipment is in order, and that everything is tuned up and the choke working properly. Does this truck have EGR and\or a smog pump?
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I dont think it has egr , I just got an oil change, flushed radiator, changed plugs and wires, new air filter. I thinking I could just maybe turn down the mixture so i didn't have so much raw fuel in my exhaust. I am tying to avoid the repair shop. I dont really know what else to do to tune it up.
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
If all you're failing is idle, EGR won't matter anyway. You can try putting the mixture screws in some to lean out the mixture; also raising the idle speed can help you pass. Before you change anything, though, make sure your choke isn't sticking.
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MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
That sounds like a stuck choke. When the motor is warmed up and idling, pull off the air cleaner lid and make sure the choke is all the way open. Are you dumping black smoke? You could have a blown power valve as well.
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From: Gadsden Purchase
I don't like this post I'm writing anymore than you do. :/
Take it to a shop that specializes in making the pickup pass.
Pay them cash.
Watch what they do, then watch what they do when they tell you
to bring it back so you can drive it home.
Next year, do it yourself for free.
BTDT for years and years.
You might stumble across the right mixture to correct the problem.
I'm betting you ain't going to. ;)
How much does a test cost?
And how many times do you get to retest for free before they charge
you again?
I'd rather give 4 times that in cash to a guy helping me out that to
the gov't to screw with me for no good reason other than money.
YMMV on that.
Alvin is just another libertarian with a bad attitude in AZ
ps- I was told and shown...
1) change the oil just a day or less before test time! <--- !
2) don't turn the vehicle off while waiting in line
3) pull the PVC hose and hide it (no use sucking oil fumes into the engine)
4) turn the idle mixture screws all the way in (gently "bottom" them)
5) adjust the idle for about 750 to 800 rpm (works great on a manual)
6) if you've got an automatic, kick yourself around the block. Twice. ;)
7) if my crap don't work, find out what does and post it in this thread :)
Take it to a shop that specializes in making the pickup pass.
Pay them cash.
Watch what they do, then watch what they do when they tell you
to bring it back so you can drive it home.
Next year, do it yourself for free.
BTDT for years and years.
You might stumble across the right mixture to correct the problem.
I'm betting you ain't going to. ;)
How much does a test cost?
And how many times do you get to retest for free before they charge
you again?
I'd rather give 4 times that in cash to a guy helping me out that to
the gov't to screw with me for no good reason other than money.
YMMV on that.
Alvin is just another libertarian with a bad attitude in AZ
ps- I was told and shown...
1) change the oil just a day or less before test time! <--- !
2) don't turn the vehicle off while waiting in line
3) pull the PVC hose and hide it (no use sucking oil fumes into the engine)
4) turn the idle mixture screws all the way in (gently "bottom" them)
5) adjust the idle for about 750 to 800 rpm (works great on a manual)
6) if you've got an automatic, kick yourself around the block. Twice. ;)
7) if my crap don't work, find out what does and post it in this thread :)
